Opening and trying to fix a leaked HP 48S

[ytterligare]

Long story short : after 6 years and a divorce, finally I got again ownership of some boxes of "toys" I left in the old home where ex-wife reside. Don't ask, I know.
BTW, a box contained my collections of HP Calculators...I'd say a pretty good collection af almost all HP models.
Now, call me fool, or maybe it was just the hurry to quit, during the inspection I noticed that two calculators, a 48sx and a 48s still had the battery in...and they leaked. The horror.

Well, I estimated on a scale of 1 to 10, the damage was 4 on the SX and 5 on the S.
After scratching and polishing the battery terminal and the plastic with Isopropylic alcohool, the sx came back to life...the joy !
But...the 48s did not : no matter how well I did polish it, the damn thing won't turn on.
I have tried any known combination of paper clip and key pressed, plus tried alkaline and eneloop batteries, no joy.
I also watched a couple of video claiming that some old 48's refuse to turn on unless you press a zone inbetween the "A" and "B" keys....tried several times with no luck.

Decided then to open the calc, and check if the leakage did something to the PCB.
Came across this article which (almost) carefully explained how-to. :

https://documents.epfl.ch/users/f/fr/fro...20HP48.pdf

Well, I generally I'm afraid to open old calcs, but what did I have to lose..? So....






As you can see, I made through step 1 and 2 somehow...but...step 3 seems impossible to me..: how do I "First, unhook the positive battery terminal from the battery compartment. " ???
I'm stuck. I cannot seems to be able to pop the remaining 6 rivets...partially because I believe the battery terminals are preventing it..





Anyone can explain how to "unhook the positive battery terminal" ? Any other suggestions ?

And anyway, how is it possible that the leakage did something to the pcb if the pcb did not reach that far, under the batteries ( see lower part on following internet pic ) ?



Thank you
A.

P.S: sorry for my writing, I'm not english native speaker.